1. Field of the Invention
This invention pertains generally to radar systems, and more particularly to a sub-carrier successive approximation radar for 3D imaging.
2. Description of Related Art
Radar based automotive and object detection systems have gained increasing attention in recent years. Adding to this interest are applications which employ millimeter (mm) wave radar techniques to construct short range three-dimensional (3D) imaging for security screening and biomedical applications. Currently, these forms of mm-wave imagers have only been demonstrated using III-V technology, because CMOS-based radars suffer several range, resolution and accuracy limitations due to limited output power and linearity.
There are numerous radar systems for automotive and aerospace purposes that are based on Frequency-Modulated Continuous-Wave (FMCW) techniques. However, the resolution and accuracy of FMCW systems are typically limited by radar sweep linearity. In FMCW ranging, the carrier is swept to produce a frequency offset at the receiver output proportional to the round trip distance between the radar and target. Although FMCW could be a good approach for accurate ranging, implementation is particularly difficult at high frequencies because the resolution is heavily dependent on sweep-linearity and the high RF front-end performance required to support the wideband swept carrier. For 3D mm wave imaging applications, this high operating frequency is indispensable as the attainable spatial resolution is fundamentally limited by the wavelength of the imaging system. The use of higher frequencies also leads to relaxed focusing lens requirements, as the optical diffraction limit is set by the ratio of the radar wavelength over the lens aperture size.
Therefore, a need exists for mm-wave short range three-dimensional (3D) imaging systems that have increased accuracy while being more easily and cost-effectively implemented.